Update building_noise_models.ipynb (#606)

typos

Author: ewinston

qiskit/aer/building_noise_models.ipynb

@@ -94,9 +94,9 @@
     "| `amplitude_damping_error` |  A single-qubit generalized amplitude damping error channel given by an amplitude damping parameter $\\lambda$, and an excited state thermal population $p_1$. |\n",
     "| `phase_damping_error` |  A single-qubit phase damping error channel given by a phase damping parameter $\\gamma$ |\n",
     "\n",
-    "### Combinging quantum errors\n",
+    "### Combining quantum errors\n",
     "\n",
-    "`QuantumError` instances can be combined to using composittion, tensor product, and tensor expansion (versed order tensor product) to produce new `QuantumErrors` as:\n",
+    "`QuantumError` instances can be combined by using composition, tensor product, and tensor expansion (reversed order tensor product) to produce new `QuantumErrors` as:\n",
     "\n",
     " * Composition: $\\cal{E}(\\rho)=\\cal{E_2}(\\cal{E_1}(\\rho))$ as `error = error1.compose(error2)`\n",
     " * Tensor product: $\\cal{E}(\\rho) =(\\cal{E_1}\\otimes\\cal{E_2})(\\rho)$ as `error error1.tensor(error2)`\n",